Electromagnetic artificial heart having control means responsive to changes in blood pressure and body respiration rate



Sept. 21, 1965 R. J. PRESTON 3,206,768

ELECTROMAGNETIC ARTIFICIAL HEART HAVING CONTROL MEANS RESPONSIVE TOCHANGES IN BLOOD PRESSURE AND BODY RESPIRATION RATE Filed June 1, 1962 2Sheets-Sheet 1 PUL MOIV/7/Q Y A o IIIIIII/IIIIIII 1/54/00; PEEJJK/E6EKG/WW6 W/A/0/A/6 N VE N TOR RICHARD J. PRESTON AGE-NT R. J. PRESTON3,206,768 ELECTROMAGNETIC ARTIFICIAL HEART HAVING CONTROL MEANSRESPONSIVE TO CHANGES IN BLOOD PRESSURE AND BODY RESPIRATION RATE 2Sheets-Sheet 2 INVENTOR RICHARD J. PRES TON BY (9040M a: BMW

AGENT Sept. 21, 1965 Filed June 1, 1962 United States Patent Thisinvention relates to an artificial heart, and in particular to the useof a pump as a replacement for or as an aid to the heart in transportingblood through the body.

In recent years great advances have been made in the medical field,particularly in work with the heart. Openheart surgery has now becomecommon, and medical and .electronic aids are now extensively used to addyears of life to damaged or defective hearts. Artificial organs are nowwell known, as are newly developed heart-lung machines which perform thefunctions of these organs during surgery. Another advance has been theuse of electronic equipment implanted within the human body to performfunctions such as supplying electronic im ,pulses to the heart, therebyregulating the rate of heart beat. Many of these advances have beenbrought about through the development of subminiature electronics andelectronic equipment, miniature power supplies and advances inmaterials. The primary advance, however, has been the increase inknowledge of the workings of the ,human body through research andexperimentation.

The present invention involves the application of the recent advances inboth engineering and medicine to thereby allow the complete replacementof a human heart by the substitution of an electromechanical pump whichwill perform the same function in the human body as the heart performs.Recent developments in electromagnetic pumps have shown that such pumpscan presently be designed with a size and efficiency which will allowtheir use as a permanent replacement for the heart.

It may also be desired to utilize such pumps to assist the heart in itsfunction of pumping blood through the body. Small pumps may be insertedin the circulatory system of man to supply more blood to desiredportions of the body when it is found that the biological system isdeficient.

An artificial heart blood-pumping device may also prove invaluable inaugmenting the heart during operations or during the extremes of spaceor planetary travel.

It is, therefore, an object of this invention to provide a system andapparatus for replacing or aiding the heart by completely or partiallytaking over the operation of pumping blood through the circulatorysystem.

Another object of this invention is the use of an electromagnetic pumpto replace or augment the heart.

A further object of this invention is a system and apparatus fordelivering additional blood to particular parts of the human body.

Another object of this inventionis a system for regulating the pumpingaction and the supply of blood through the human body when an artificialheart or auxiliary blood pump is used.

A further object of this invention is an apparatus and system usedoutside the body to profuse portions of the body during experiments inpartial or profound hy- .pothermia.

These and other features and advantages will be apparent from thespecification and claims, and from the accompanying drawings whichillustrate an embodiment of the invention.

FIGURE 1 is a schematic representation of the human circulatory systemwith a pump substituted for the heart; and

FIGURE 2 is a schematic drawing of a typical electromagnetic pump; and

FIGURE 3 is a functional block diagram of an electronic system foroperating an artificial heart.

The human circulatory system supplies the muscles, nerves and tissueswith blood, the blood carrying necessary elements to the tissues andwithdrawing waste products. The digestive system supplies the blood withnourishment and the respiratory system provides the blood with oxygenand allows certain waste to pass from the body. FIGURE 1 showsschematically a portion, of the circulatory system. The blood flowsalong a closed system of tubes from the heart to the arteries,capillaries and veins. The center of the circulatory system is theheart, which lies in the chest between the two lungs and above the sheetof muscle known as the diaphragm. The heart is really a portion of thecirculatory system tubing, with greatly enlarged channels and thickenedwalls. The heart receives the blood from veins, sends it to the lungs,receives it back from the lungs and then pumps it through the arteries.

The circuits through which the blood flows in the body may be dividedinto two broad groups comprising first, the arteries which transport theblood to the remote portions of the body into the capillaries, andsecond, the veins which transport the blood back from the capillaries tothe heart.

Referring particularly to FIGURE 1, a pump 10 has been substituted forthe heart in the circulatory system. The blood is received from thevarious extremities: of the body through two large veins called thesuperior vena cava and inferior vena cava which feed the used blood tothe pump 10. As will be explained later, the pump may be controlled toprovide a pressure to the blood at a rate equivalent to that of thehuman heart. The blood then proceeds out of pump it) through thepulmonary artery to the lungs where an exchange of oxygen and carbondioxide takes place. The oxygenated blood which leaves the lungs throughthe pulmonary vein is shown connected directly to the aorta whichthereupon transports the blood to the other portions of the body. Thepump 10 may also be inserted into the circulatory system after the lungsrather than before the lungs. This cycle takes approximately one minute.In the human heart, the blood flow is'from the veins to the right sideof the heart, out of the heart and through the pulmonary artery to thelungs, out of the lungs to the left side of the heart, and then ispumped out of the heart and through the aorta to the body.

While it is apparent that a single pump can supply sufficient pressureto push the blood through the lungs and also through the completecirculatory system, it appears preferable to return the blood from thelungs to either an addition-a1 pump or "o a dual channel of pump 10. Theadditional pumping action may be necessary to prevent the rupturing ofthe lungs by the higher pressure required if only one pump is used, andthe use of two pumping stages appears desirable. If necessary, thesecond pumping stage would be inserted after the lungs to pump theoxygenated blood into the aorta, and thence to the arteries.

The pump required as a replacement for the heart must meet severalrequirements. First, the pump must be leakless. Second, the pump musthave an exceptionally vhigh degree of dependability such as might beobtained with a device having no moving parts to wear out. Third, thepump must be reasonably eflicient and must be capable of fitting into asmall space. Fourth, the pump must be capable of operating with lowpower dissipation.

The electromagnetic pump meets all the requirements enumerated above.FIGURE 2 shows schematically a typical electromagnetic pump. Allelectromagnetic pumps utilize the motor principle, that is, a conductorin a magnetic field, carrying a current which flows at right angles tothe direction of the field, having a force exerted on it which ismutually perpendicular to both the field and the current. In thesepumps, the fluid, blood in this case, is the conductor. The force,suitably directed in the fluid, manifests itself as a pressure if thefluid is properly contained. The field and the current can be producedin different ways and the force may be utilized in different ways. Thereare a number of different types of electromagnetic pumps, all of themusing this principle.

The blood has been found to be somewhat conductive in its natural state.Conductivity can be added to the blood by introducing an iron complexsuch as ferric chloride. This may take the form of capsules orinjections. If too much iron is added to the blood, the excess will beexcreted.

The most elementary electromagnetic pump has been called the Faradaytype shown in FIGURE 2. In this pump, the fluid is contained in athin-walled duct. A constant magnetic field is passed through the fluidon one axis perpendicular to the direction of flow. The field isdeveloped by a winding, D.C. excited, arranged on a suitable magneticcore which provides both pole faces and a magnetic return path. Currentis forced through the fluid by impressing a voltage across the axis ofthe duct mutually perpendicular to both the field and the direction offlow. The operation of the pump is similar to a DC. shunt motor. Theseparately excited field magnetizes the gap. Flow of the current in thefluid in the gap is similar to current in a DC. motor armature. An 1 Rloss appears in the fluid. As the fluid flows a back voltage or isgenerated by the fluid moving in the field, opposing the flow of currentin the fluid. The product of the back voltage and the effective currentin the fluid represents the pumping power developed.

The Faraday pump can be made to work on alternating current when thefield is excited by A.C. properly phased with the voltage applied to thearmature. These A.C. pumps are similar to the pump shown in FIGURE 2.However, the A.C. version of the Faraday pump has a lower efliciencythan the DC. pump since the fluid acts as a shorted turn in thetransformer.

A helical flow induction pump requires guide veins in the ducts, butthese pumps are well suited for high pressure, low-flow applicationswhere space is at a premium and are attractive for use as a replacementfor the heart.

The linear induction pump is a modification of the helical pump andprovides large flow at moderate heads for limited space and power supplyand is also attractive for heart application.

Engineering Magazine, April 27, 1956, contains an article entitledElectromagnetic Pumps, at page 264 which describes in detail thedifferent types of electromagnetic pumps, the theory of operation andthe manner in which losses and efliciencies may be computed.

Recent studies have shown that any of the above types of electromagneticpumps can be developed small and light enough to replace the heart inthe human body. The efliciency of such a pump would be aproximately 40%.

The weight of the average human heart is between 1000 and 1500 grams(2.2 lbs. to 3.7 lbs.). An artificial heart of five lbs. could behandled easily by a human being. The maximum chest cavity spaceavailable for a heart replacement, if the diaphragm is partially cutaway,

is six inches in diameter by twelve inches long. The back pressure ofthe biological circulatory system as felt by the heart varies betweenminus five to plus fifteen centimeters of H 0. The average pressure inthe human heart is between 100 to 180 millimeters of mercury. The

average rate of flow of blood in the human circulatory system averagesbetween four to fifteen liters per minute, and may go as high aseighteen liters per minute for an untrained person under stress andtwenty-five liters per minute at a severe stress peak for a trainedathlete.

Development work on electromagnetic pumps has shown that pumps of thesize, weight, efliciency and capacity required to replace the heart canbe produced. The channel of the pump should preferably be flat and widefor optimizing the design and efficiency of the pump.

The specific resistance of whole blood at 37 centigrade has beencomputed as a function of frequency. The chart below shows the resultsof the experimentation.

Specific resistance Frequency: (OhITl/CHl-g) c.p.s 166 1 kc. -180 1 me100 me. 80-100 1000 me. 64-80 10,000 mc. 93-11 pump 10 for the purposeof illustrating that the pump 10 may either completely replace the heartor serve as an aid to the heart. The pump may be placed in parallel withthe heart or a small pump may be located any place within the arterialsystem to pump additional blood to whatever part of the body is in needof more blood.

FIGURE 3 also shows, in block diagram form, a typical electronic controlsystem for regulating the pumping action of the pump 10.

A transducer 20 is connected to a vein to sense venous pressure rate. Ithas been found that pressure waves are created in each beat of theheart, and this pressure rate may be sensed in either the arteries orthe veins. It appears Preferable to sense this pressure at a veinprimarily because of the danger involved with arterial penetrations.FIGURE 1 shows the venous pressure transducer 20 connected to a veinleading into the inferior vena cava. Any vein may be used, but a veinadjacent the heart appears to be preferable since it would be moreconvenient at that point. An optimized location giving easy access to avein is where the leg joins the bottom of the trunk.

The venous pressure rate transducer 20 and the other electronic circuitsto be described will preferably be implantable molecular circuits.Recent advances in molecular circuitry has shown that such circuits maybe constructed of very small size and low power dissipation. The venouspressure rate sensor itself will P eferably be a tunnel diode crystalwith venous pressure acting upon the junction to shift the frequency ofoscillation of the crystal as a function of the pressure. Anotheroscillator may be used for the venous pressure rate set 22. Thisoscillator 22 will produce an A.C. signal which is a function of thedesired pumping rate for pump 10. The oscillator signals from both thepressure rate transducer 20 and the pressure rate set 22 are fed to asumming network 24 which may be a beat frequency generator network wherean A.C. error signal is generated having a frequency proportional to thedifference between the pressure set and the actual venous pressure rate.This error signal is amplified by amplifier 26 and fed to a frequencyconvertor 28 which transforms the AC. error signal into an AC. signalproportional to the error signal.

The output of the frequency convertor 28 is fed to a control circuit 30which controls the application of the magnetic field from magnetic powersupply 32 to pump 10. A current power supply 34 provides current to pump10. As shown in FIGURE 2, the magnetic field and current are at rightangles to each other and orthogonal to the blood flow. Since currentthrough the blood may have a tendency to ionize or dissociate the blood,it is desirable to keep the pump current at a minimum value. It has beenfound that ampere per cm. through the blood will not cause any harmfuleffects. If the conductivity of the blood and the pump current are keptconstant, variations in the magnetic field intensity may be used to varythe pumping rate of pump 10. Thus, it is preferable to use the signalfrom control circuit 30 to vary the magnetic field strength supplied bymagnetic power supply 32 to pump 10. The power supply 34 will supplyconstant current to pump 10. It is clear that, depending on the type ofpump used, a DC. system or control signal may be preferred. If block 28were to be replaced by a discriminator, the DC. could be easilysupplied.

Pump 10 may also be operated by keeping the magnetic field constant andvarying the current as a function of the error signal. Likewise, bothmagnetic field and current may be varied. The particular pump used willinfluence the choice of the parameter to be varied and also theparticular circuits used in the control system.

The electronic control system thus far described is typical of manyservo systems and is adequate to keep pump 10 operating at a fixed rateto thereby supply a relatively constant volume of blood through thecirculatory system. However, the heart does not pump a constant volumeof blood through the circulatory system, but the volume in fact variescontinuously depending on the needs of the body. Thus, under extremestress conditions a much greater volume of blood is required to supplyoxygen to the body organs. A respiration rate transducer 36, which isresponsive to respiration rate, can be used to change the set point ofthe venous pressure set 22. Respiration rate has been found to vary indirect proportion to metabolic activity. Now when more oxygen isrequired by the various parts of the body and the lungs are required towork harder, the human inhales more oxygen, and rate transducer 36 willsense this increased respiration rate and vary the set point to create alarger error signal and force pump 10 to pump more blood throughout thebody. The transducer 36 may consist of two electrodes inserted into themuscular tissue of the chest wall adjacent the lungs, and the impedancechange due to lung action will give a measure of respiration rate.Amplification of this signal may be necessary. A tank-type circuit mayalso be used.

Although the disclosed system uses heart or pump rate for control, theblood pressure must also be considered. Blood pressure increases withrate, so that a higher rate will give a higher pressure. The veins andarteries expand somewhat with pressure, and can readily withstand anypressure increases within the rates which occur in the pump. Recent workwith animals has shown that a constant blood pressure is not harmful,and indicates that a constant pressure blood supply may be used by man.

FIGURE 1 shows a block 38 labeled electronics. This block contains allthe electronic circuitry as shown in FIGURE 3 including power supplies32 and 34. FIG- URE 1 also shows that venous pressure transducer andrespiratory rate transducer 36 provide control signals to block 22.These control signals may be telemetry signals, which eliminates theneed for wires within the body. Block 38 is connected directly to pump10.

Because of the fact that the veins are located at a distance through thecirculatory system from the heart, the pressure wave sensed in any veinis necessarily delayed from the beat of the 'heart which produced thepressure wave. A time delay may be introduced into the system byproviding either an anticipation circuit or a lag cir- 'cuit in thesumming network or pressure transducer to compensate for the time delay.The power supply for pump 10 may be a small battery such as used in thePacemaker, but the battery may need to be larger since more power isneeded to operate the pump then is needed to stimulate the heart. Othertypes of power supplies may be used, for example, those which use thebody heat to power thermoelectric supplies, chemical power supplieswhich utilize the body chemistry, or biological fuel cells using thestomach as a generator, or muscle power in which muscle movement is usedfor power. A particular type of power supply under development is thetransponder which radiates by means of RF energy power through anantenna located internally which thus provides suitable power to thepump.

The heart contains at least two major valves which close after each beatto prevent the blood pumped by the heart from pushing back into theheart chamber from which it was pumped. Pump 10 does not need this typeof check valve. A bias may be provided to the magnetic field or currentsupply of the pump so that a minimum forward pressure is alwaysproduced.

The control circuitry of FIGURE 3 has been described as A.C. circuitry,but it is obvious that DLC. circuitry may also be used. The electronicsand the control system are well known and the actual circuits used willobviously depend upon the pump and the power supply. However,alternating current operation of the pump is preferred primarily becausethe specific resistance of the blood decreases with the frequency sothat it is advantageous to use as high a frequency as possible.

Any heat which is generated in either the pump or the electronics may betransferred through the blood to the skin or neutralized by means ofthermoelectric cooling unctions.

It is apparent that since a pump can be used to replace the heart, thesame type of pump may be inserted anywhere within the body to assist theheart or the arteries for supplying blood to the organs. For example, itwould be advantageous to profound hypothermia to pump blood and profusethe brain through the carotid. artery and ugular vein while the rest ofthe body was in a state of profound hypothermia and suspended metabolicactivity.

The electromagnetic artificial heart can be useful in both implant andextra-corporeal capacities, the latter primarily during operations andduring space travel. While this description is primarily directed toimplant uses for such an artificial heart, extra-corporeal uses, withsimilar control techniques, may also be desirable.

Numerous changes may be made in the components and circuitry, as forexample using different types of pumps, without departing from the scopeof this invention.

I claim:

1. Apparatus for delivering blood to at least a portion of thecirculatory system of a living body comprising an electromagnetic pump,means for connecting said pump in a blood conducting passage of thecirculatory system of a living body, actuating means for said pump, meanfor producing a signal indicative of the actual blood pressure in saidsystem, means for producing a reference signal indicative of desiredblood pressure, means for comparing said actual blood pressure signalwith said reference signal to produce an error signal proportional tothe ditference between said desired blood pressure and said actual bloodpressure, means conducting said error signal to said pump actuatingmeans to vary the rate of said pump and eliminate said error signal, andmeans for varying said reference signal in response to changes in therespiration rate of said body.

2. Apparatus as in claim 1 in which said means for producing a, signalindicative of actual blood pressure comprises an electronic sensoradapted to be connected to a vein for said body and responsive topressure variations in said vein.

3. Apparatus as in claim 2 in which said means for varying saidreference signal in response to changes in the respiration rate of saidbody comprises a transducer having a pair of electrodes adapted to beinserted into the muscular tissue of the chest wall of said bodyadjacent the lungs.

4. Apparatus as in claim 3 in which said pump comprises a duct adaptedfor fluid flow therethrough, a magnetic core having windings thereon toprovide a magnetic field perpendicular to the direction of fluid flow,

8 and means to produce a voltage across said duct mutually perpendicularto said fluid flow and to said magnetic field, said error signal beingapplied to said magnetic core windings to vary the magnetic fieldstrength and thereby vary the rate of said pump.

5. Apparatus as in claim 4 in which a constant bias signal is generatedin said pump magneticcore field windings to thereby produce a minimumforward pressure to said fluid and prevent reverse fluid flow throughsaid pump.

References Cited by the Examiner UNITED STATES PATENTS 2,917,751 12/59Fry 3-1 2,925,814 2/60 Vibber 128214 3,066,607 12/62 Cole 1031 RICHARDA. GAUDET, Primary Examiner.

1. APPARATUS FOR DELIVERING BLOOD TO AT LEAST A PORTION OF THECIRCULATORY SYSTEM OF A LIVING BODY COMPRISING AN ELECTROMAGNETIC PUMP,MEANS FOR CONNECTING SAID PUMP IN A BLOOD CONDUCTING PASAGE OF THECIRCULATORY SYSTEM OF A LIVING BODY, ACTUATING MEANS FOR SAID PUMP,MEANS FOR PRODUCING A SIGNAL INDICATIVE OF THE ACTUAL BLOOD PRESSURE INSAID SYSTEM, MEANS FOR PRODUCING A REFERENCE SIGNAL INDICATIVE OFDESIRED BLOOD PRESSURE MEANS FOR COMPARING SAID ACTUAL BLOOD PRESSURESIGNAL WITH SAID REFERENCE SIGNAL TO PRODUCE AN ERROR SIGNALPROPORTIONAL TO THE DIFFERENCE BETWEEN SAID DESIRED BLOOD PRESSURE ANDSAID ACTUAL BLOOD PRESSURE, MEANS CONDUCTING SAID ERROR SIGNAL TO SAIDPUMP ACTUATING MEANS TO VARY THE RATE OF SAID PUMP AND ELIMINATE SAIDERROR SIGNAL, AND MEANS FOR VARYING SAID REFERENCE SIGNAL IN RESPONSE TOCHANGES IN HE RESPIRATION RATE OF SAID BODY.